General relativity predicts that gravitational waves should have two helicity-2 polarization states. However, a generic metric theory of gravity allows up to four additional states: two helicity-1 and two helicity-0 modes. Observations of gravitational waves allow tests of this basic prediction of general relativity. In this talk I will review three tests of gravitational wave polarization, using Advanced LIGO and Virgo. First I will discuss a polarization test from GW170814 event. Next, I will discuss tests based on emission from rotating pulsars, which emit continuous, periodic gravitational waves. Finally, I will discuss a search method for a stochastic background of scalar and vector polarizations.